Boll-weevil sex attractant

ABSTRACT

Synthetic routes to each of four critical components of the boll-weevil sex attractant complex are described. Effective mixtures of the several components equal to or better than the natural attractant are disclosed.

United States Patent Gueldner et al.

BOLL-WEEVIL SEX ATTRACTANT Inventors: Richard C. Gueldner, Starkville;

James H. Tumlinson, West Point; Dicky D. Hardee, Starkville; Paul A. Hedin, Starkville; Alonzo C. Thompson, Starkville; James P. Minyard, State College, all of Miss.

The United States of America as represented by the Secretary of Agriculture, Washington, DC.

Filed: May 14, 1973 Appl. No.: 360,280

Related U.S. Application Data Division of Ser. No. 248,183, April 27, 1972, abandoned, which is a division of Ser. No. 90,794, Nov. 18, 1970, abandoned.

Assignee:

U.S. Cl 260/617 R; 204/162; 260/635 R; 260/635 Y; 260/642 R; 260/643 G; 424/84 Int. Cl. C07c 33/02 Field of Search 260/617 R, 635 R, 635 Y, 260/643 G, 642 R; 204/162 [451 July 15, 1975 OTHER PUBLICATIONS Cram et al., Organic Chemistry, p. 74 & 75, P315 (1964).

Primary ExaminerDonald G. Daus Assistant ExaminerD. B. Springer Attorney, Agent, or FirmM. Howard Silverstein; Max D. Hensley [5 7 ABSTRACT Synthetic routes to each of four critical components of the boll-weevil sex attractant complex are described. Effective mixtures of the several components equal to or better than the natural attractant are disclosed.

1 Claim, No Drawings BOLL-WEEVIL SEX ATTRACTANT A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This is a division of application Ser. No. 248,183 filed Apr. 27, 1972, now abandoned, which was a division of Ser. No. 90,794, filed Nov. l8, 1970, now abandoned.

This invention relates to the control of boll weevil infestations, particularly in cotton, by utilization of a synthetic mixture of components which are identical to, or simulate, in chemical structure, the natural components elaborated by the insects as a sex attractant and aggregant.

The main object of the instant invention is to provide a means of concentrating an insect population so that pesticidal or biological means of control are more efficient, more specific to the target insect, and less likely to cause damaging ecological disturbance of other spe cies. in particular this invention concerns the control of the boll weevil in cotton 'fields.

Another object of the instant invention is to provide a novel. effective means of boll weevil control which constitutes an improvement over existing methods of control.

A third object of the instant invention is the elucidation of the structures of the natural sex attractant/aggregant components.

A fourth object is the disclosure of a process for synthesis of key precursors and the final compounds which make up the sex attractant/aggregant complex.

A fifth object is the formulation of a mixture of the synthetic compounds which has attractant power simulating or surpassing the live male insects.

The boll weevil is the most serious pest of cotton in the United States, necessitating the use of about $75 million worth of insecticides in 1968 and causing an estimated annual loss of $375 million. The larval stage of the insect developing in the cotton bud causes loss of the fruit and consequent decrease in fiber production.

2 The life cycle of the insect is completed when the adult male, feeding on the cotton plant, elaborates the compounds composing the sex attractant/aggregant complex, fertilizes the eggs of the adult females lured by the scent, and the fertilized eggs are deposited in the cotton bud.

Insecticides have been used to control the insect population by broadcast application over entire fields. The increased resistance of the insect survivors progeny require higher levels of insecticide per acre to maintain comparable control from year to year. The widespread application of insecticides may harm beneficial insects, birds, and fish from the resulting environmental pollution.

It has been demonstrated that attractancy of adult male weevils to female weevils and to both sexes exists during the spring and fall, Furthermore it has been shown that this attractancy can be extracted from the boll weevils and from the insect feces.

We have found that the extract components responsible for the attractancy isolated and identified by chemical and spectra] means, are cis-Z-isopropenyl-lmethylcyclobutaneethanol, Leis-3 ,3-dimethyl-A cyclohexaneethanohl I ,cis-3 ,3-dimethyl-A cyclohexaneacetaldehyde,IlI, and trans-3,3-dimethyl- A -cyclohexane-acetaldehyde, IV.

When the above four compounds (synthesized as shown in the examples which follow) are combined in an optimum ratio, females respond equally or better than they respond to live male weevils in laboratory bioassays.

EXAMPLES Synthesis of Compound I and lsomers Isoprene, (150 ml), methyl vinyl ketone ml), and acetophenone (20 ml) were placed in a 250 ml reaction vessel which contained a high pressure, quartz, 450 watt, mercury vapor photochemical immersion lamp inserted in a quartz well which well was cooled with water to about 5C. A pyrex cylinder filter surrounded the lamp. The mixture was irradiated with light from the inserted lamp for about 144 hr. During this time considerable polymer formed and it was necessary to cis trans V VI cis and trans 1,3

VII

Calc'd. (178.21. H. 10.21.

Elemental analyses arc:

Found: C. 8.08; H. 10.l4.

Methyl magnesium iodide was prepared in the usual manner in dry ether. The appropriate ketone (V. VI. or Vll) in dry ether was added drywise to a slight molar excess of MeMgl. cooling. if necessary in a water bath. After addition of the ketone was complete, the reaction mixture was refluxed gently for 1 hr. It was then cooled in ice-water and a saturated NH Cl solution was added slowly until no further reaction occurred. This was evident by formation of a white precipitate and no foaming on addition of more NH Cl solution. The mixture was allowed to stand 30 minutes, the ether decanted, and the contents of the flask washed twice with ether. The combined ether extracts were dried over Na- SO, or alternatively MgSO the ether evaporated, and the products purified by GLC. Ketones V. VI, and VII yielded alcohols Vlll, lX. and X respectively.

Structures were determined by NMR, IR, and mass spectroscopy.

Elemental analyses are:

Vlll: Calcd for Cm OI Found:

The appropriate tertiary alcohol, Vlll, lX, or X was placed in a three neck round bottom flask equipped with a condenser and magnetic stirrer. Dry N was introduced in one side arm and removed through the condenser which was connected to an acetone wash bottle to remove excess B- H The center neck of the flask was fitted with a rubber septum through which samples and reagents were introduced by means of syringes. A conventional hydroboration reaction was then carried out as follows. To 0.03 mole of the alcohol in the flask was added 0.009 mole of sodium borohydride in diglyme (0.0 ml of L0 M solution in diglyme). To this 0.012 mole of freshly distilled BF etherate was added slowly.

A static pressure of N was maintained during the reaction. The reaction mix was allowed to stand at room temperature 1 hr. and then hydrolyzed with 2 ml H O. When H was no longer evolved 4 ml of 3N NaOH was added and then 4 ml of 30 percent H 0 dropwise so as to maintain a gentle reflux. The reaction was allowed to cool, and ether was added to the flask. Solid NaOH was added to form a layer in the bottom of the flask. The ether was decanted and the flask washed twice more with ether. The ether extracts were combined, the ether evaporated. and the diols purified by GLC for analysis. Tertiary alcohols VIII and IX yields diols XI and Xll respectively.

Alcohol X which probably also consisted ofa mixture of cis and trans isomer yielded two diols. XIII and XIV.

The structures of the diols were determined by NMR, IR, and mass spectrocopy.

The diols in diglyme were dehydrated without purification. A slight molar excess of acetic anhydride was added to the diglyme solution of the alcohol and the mixture was refluxed for 3 hours. During this time samples were removed for GLC analysis to determine the extent of progress of the reaction. Initially, a peak with a much longer retention time on SE-3O replaced the diol peak and then this gradually disappeared with another peak with retention time near that of the diol arismg.

Reduction of this mixture with LiAlH yields the primary unsaturated alcohol. Thus the following sequences of reaction produce the products indicated.

V VIII XI I V! IX )XII trans V XV his CH OH XVI trans Structures were confirmed by NMR, mass, and IR spectral studies.

Calcd. for C H O: C, 7 7;

Elemental analyses are: 7 8

Found: C. 77.63;

Compound I is identical in every way, including biological activity to the natural component of the sex attractant isolated from weevils and their fecal material.

3 ,3-Dimethylcyclohexanone Ethy1-( 3 .3-dimethyll -hydroxycyclohexyl )acetate To 48.5 g. (0.743 moles) zinc was added, with heating and stirring, a mixture of 124.2 g. (0.742 moles) of ethylbromoacetate and 31.3 g. (0.248 moles) of 3.3-dimethylcyclol1exanone in 300 ml. dry benzene. After the addition period of 1.5 hrs., the mixture was stirred and refluxed for 5 hrs. The flask was cooled in an ice bath and 450 ml. of 10 percent sulfuric acid was added. in a separatory funnel the aqueous layer was removed from the benezene layer. The benzene layer was washed alternately with 5 percent sulfuric acid and 10 percent sodium carbonate solutions, and finally with water. The benzene solution was dried over sodium sulfate and the benzene was removed by distillation. The residue of 59.2 g. was distilled in vacuo to yield 31.7 g. 159.6 percent) boiling at 1l21 13 C. at 5.4 mm. hg.

Anal.; Calc d. for C r-z -zz a Found:

3,3-Dimethyll -hydroxycyclohexyl acetic acid To 20 g. potassium hydroxide in ml. water was added 15.0 g. (0.07 moles) of ethyl-(3,3-dimethyl-lhydroxycyclohexyl) acetate. The mixture became homogeneous in 3 hours. After extraction with ether the aqueous basic solution was acidified and the precipitated acid was collected by filtration and dried over phosphorus pentoxide for 16 hours. The dried acid was recrystallized from benzene to give 11.0 g. (84.6 percent) m.p. 1091 10 C.

Calculated for C H O z Found:

C. 64.49; H. 9.74. C, 64.55; H. 9.75.

Dehydration of 3, 3-Dimethy1- 1 -hydroxycyclohexyl-acetic acid The hydroxy acid (43.2g) was refluxed in ml acetic anhydride for 5 /2 hrs. Most of the acetic anhydride was then removed by distillation. Part of the residue (33.4 g.) was subjected to basic hydrolysis in 20 percent KOH for 30 minutes. The basic solution was cooled and acidified and then extracted with chloroform. The chloroform extract was dried and concentrated to 24.0 g. Crystallization of the 24.0 g. from pentane yielded 15.1 g. mp. 6085 C., a mixture of isomers of the unsaturated acids.

Esterification of the unsaturated acids Calculated for C H Q Found for cis ester: Found for trans ester:

C, 73.42; H, 10.27. C, 73.55; H, 10.38. C, 73.42; H, 10.39.

Method B Methyl esters The mixed unsaturated acids 28.4 g. were dissolved in ether and treated with excess diazomethane in 300 ml ether. The ether was removed by distillation and the residue was distilled twice to yield 12.9 of mixed esters in five fractions. The five fractions were combined and distilled through an efficient column to yield 4.5 g. of pure cis ester and 1.0 g. of pure trans ester.

Reduction of the unsaturated esters with lithium aluminum hydride The ethyl esters of both cis and trans esters were reduced and isolated in a similar manner according to the following procedure:

The ethyl ester of the cis unsaturated acid collected from gas-liquid chromatography (about 100 mg) was added to 1 g. of LiAlH in 50 ml of ether after the ether-hydride mixture had been refluxed for 1 hr. The

mixture was refluxed for 1.5 hr. cooled, and the excess 20 hydride decomposed with 10 percent NaOH. The ether solution of the alcohol was filtered. concentrated. and purified by gas-liquid chromatography. Infrared and NMR spectra showed the product to be identical with Oxidation of cis and trans alcohols to the corresponding aldehydes The example given is for the cis alcohol but the procedure is exactly the same for the trans alcohol also.

Active MnO was prepared as per Attenburrow et al., J.Chem.Soc 1094( 1952). A mixture of 100 mg of the alcohol and 3.3 g. of active MnO in 30 m1. pentane was stirred for 30 minutes at 0 C. The mixture was filtered, most of the pentane removed. and the product analyzed by gas-liquid chromatography. Chromatographically pure samples were examined by NMR, mass, and infrared spectrometry and bioassayed for activity.

The overall synthesis scheme for the unsaturated alcohol (component 11) and the cis and trans unsaturated aldehydes (components 111 and IV, respectively) is shown in FIG. 1.

Cu Cl d1 2 1 d o COOE'r COOH KOH HO d BrCH COOEt n 2m ,HZO

COOH

1) cii cm o ICOOET ETOOC ETOOC Figure 1.--Synthesis Scheme -\s an example of the activity (in the laboratory bio- LlSSkly l of the single components and cis mixtures, Table 1 summarizes the activity at optimum concentrations. Table 1. Female boll weevil response, in laboratory hioassays, to optimum concentrations of compounds 1. 11, III, IV. T/S equals net response to test sample divided by net response to a standard. The sample in each case consists of the compound, or .1 mixture of the compounds indicated, in 0.2 ml dichloromethane. The standards used were live male boll weevils or steam distillates which were equivalent in attractancy to live males.

Examples of formulations The four synthetic components combined in 0.2 ml dichloromethane solution in a ratio 0.09 .Lg, 0.12 pg, 0.12 g, 1, ll. III, IV were applied to (l) firebrick, (2) fiberboard. (3) cardboard, and these materials were used in laboratory bioassays. Another formulation for laboratory bioassay involved the placement of the dichloromethane solution in a sealed polyethylene container.

For field studies the synthetic components were presented as follows:

1. Absorbed on firebrick.

2. Absorbed on fiberboard.

3. A pipette containing the dichloromethane solution with a cotton wick protruding from the pipette.

4. The frass of weevil is treated with the dichloromethane solution.

We claim:

1. A process for producing the cis isomeric form of 2-isopropenyll-methylcyclobutane ethanol which process consists of the following steps carried out in sequence:

a. irradiating with ultraviolet light a mixture cooled to about C for about 144 hours, said mixture comprising 7.5 parts by weight of isoprene, about 4 parts by weight of methyl vinyl ketone, and about 1 part by weight of acetophenone to produce a product which comprises an isomeric mixture of ketones represented by the structures 1; C Cir: w u H r 2 \f. l 1 1 Q l 4 H, 5

\.-=O (2:0 D I CH CH3 b. distilling the product from (a) c. separating the distilled product from (b) by gasliquid chromatography to obtain the cis isomer represented by the structure l l CH c H o d. reacting the cis isomer from (c) with a slight molar excess of methyl magnesium iodide;

e. refluxing the mixture from (d) for about 1 hour;

f. cooling the mixture from (c) and saturating with ammonium chloride to give the corresponding alcohol represented by the structure j. dehydrating the diol from step (i) with acetic anhy dride in diglyme at reflux to produce the unsaturated alcohol represented by the formula 

1. A PROCESS FOR PRODUCING THE CIS ISOMERIC FORM OF 2-ISOPROPENYL-1-METHYLCYCLOBUNATE ETHANOL WHICH PROCESS CONSISTS OF THE FOLLOWING STEPS CARRIED OUT IN SEQUENCE: A. IRRADIATING WITH ULTRAVIOLET LIGHT A MIXTURE COOLED TO ABOUT 5*C FOR ABOUT 144 HOURS, SAID MIXTURE COMPRISING 7.5 PARTS BY WEIGHT OF ISOPRENE, ABOUT 1 PART BY WEIGHT OF ACETOMETHYL VINYL KETONE, AND ABOUT 1 PART BY WEIGHT OF ACETOPHENONE TO PRODUCE A PRODUCT WHICH COMPRISES AN ISOMERIC MIXTURE OF KETONES REPRESENTS BY THE STRUCTURES 